GEOLOGY OP CENTRAL WASHINGTON TERRITORY. 483 



The upper Columbia and its tributaries, through the whole route of the expedition, presented 

 this formation upon a scale of singular magnitude and variety of circumstance. It is probable 

 that in this northern district, where the winters are exceedingly cold, ice has played an import 

 ant part upon these elevated lakes ; but the surface of the country exhibits no evidence of its 

 action subsequent to their drainage, and there are no appearances either of the former existence 

 of fixed glaciers, or the transportation of boulders from a distance by moving bodies. In fact, 

 rocks out of place are of very rare occurrence, considering the mountainous character of the 

 country, and nowhere to a size or extent beyond the capacity of ordinary causes. 



On leaving the Columbia to visit the Chelan lake, our route ascended one of these terraces, 

 rising to the height of six hundred and forty feet in a single slope, and occupying a recess in the 

 hills which bordered it. On reaching the top, it proved to be the entrance of a level valley, 

 extending through the hills and emerging at about one hundred and fifty feet above the lake. 

 This valley or coulee is only one of a number noticed in this region, and is analogous to the 

 &quot;cots&quot; or &quot;land straits&quot; described by Sir Charles Lyell, (Manuel El. Geol., ch. vii.) The lake 

 is four hundred and seventy-four feet above the Columbia at its mouth, and its outlet makes this 

 descent in about four miles. It did not appear to be very deep, though it occupies a narrow 

 valley between precipitous mountains of syenite; the detritus of these having probably filled it up. 

 Its length seems, from Indian account, to be thirty-five or forty miles. It affords a good illustra 

 tion of what the other terraced valleys formerly were; the appearance of its shores indicating 

 that, should the barrier at its mouth be removed, similar terraces would remain to those which 

 border the Columbia at its mouth. 



The most remarkable exhibition of these is, however, upon the Methow river the barrier R. 

 of Wilkes s map. In crossing the mountains between Fort Okinakane and that stream, we 

 noticed, upon the summit and high up on the sides, remains of those formed previous to their 

 elevation; but the valley of the river itself is lined with others of a later date. According to two 

 or three of the barometrical observations taken in surveying the supposed pass, the altitudes of 

 these appear to agree sufficiently with some on the Columbia to indicate their connexion. In 

 descending the river, we met with two dams or barriers which had once restrained its waters, 

 and concerning which there could be no question. The first was externally a mere well of 

 detritus, though probably with a rocky foundation. It was level on the top, and sloped at the 

 sides like the lateral terraces. Half a mile below was the second, which was formed against a 

 protruding point of rocks. In both cases the river had cut merely a narrow channel through 

 them on one side, leaving the rest standing. The walls of syenite on the Methow were in many 

 places cut and smoothed by the action of the water at a height of seventy-five or eighty feet 

 above its present bed. At the mouth of the river no less than eighteen terraces, rising one above 

 another, were counted. Small moraines were noticed in this valley, but apparently rather the 

 result of violent rush of water from lateral branches than of ice. The valley of the Methow 

 affords a richer field for the geologist in plutonic and metamorphic rocks than any other portion 

 of the Territory visited by the survey, and would richly reward a careful exploration. Gneiss, 

 syenite, and granite occur, well characterized and blended with each other. The syenite is 

 often divided by joints so as almost to appear stratified, and to give its perpendicular walls 

 the semblance of artificial construction. The gneiss is found both horizontal and displaced by 

 the intrusion of trap. Associated with these are also serpentine conglomerates and prophyry. 

 Almost all these rocks pass by insensible gradations into one another, and their relative positions 

 are excessively complicated. There appears to be a very great resemblance between the 

 geology of this part of the Cascades and that of the Shasta mountains, as described by Wilkes 

 in his memoir on Western America. 



The rock in place on the Columbia between the Chelan and the mouth of the Okinakane 

 was syenite, varying somewhat in character. It was frequently intersected with large veins of 

 feldspar. In crossing from Fort Okinakane to the forks of the Methow the syenite changed to 



